The present invention relates to electronic assemblies with a heat sink.
It finds an advantageous application particularly for control modules of a motor-vehicle headlight discharge lamp.
Assembly structures with a heat sink for control modules of a motor-vehicle headlight discharge lamp have already been described, particularly in the patent applications FR 95 14.647 and FR 98 12.219.
The assemblies described in these patent applications include a metal sole plate, which constitutes a heat sink, and a printed circuit card which is assembled, for example by bonding, onto the said sole plate.
The layers used to form the bonding do not necessarily allow good thermal transfer between the printed circuit card and the sole plate.
One object of the invention is to propose an assembly structure which makes it possible to enhance the thermal exchanges between the printed circuit card and the sole plate, while being simple in construction and of low cost.
According to a first aspect of the present invention there is provided assembly including a metal sole plate forming a heat sink, as well as a printed circuit card carried by the said sole plate, wherein the sole plate includes at least two bearing surfaces which project slightly with respect to the rest of the said sole plate and on which the printed circuit is supported, the said bearing surfaces including fixing means which interact with supplementary means of the printed circuit card to fix the printed circuit card onto the sole plate, and wherein a thermally conducting and electrically insulating material is arranged in the areas between the bearing surfaces, being interposed between the said card and the said sole plate, the printed circuit card and the sole plate exerting a compression stress on the thermally conducting and electrically insulating material.
With such an assembly structure, the material interposed between the printed circuit card and the sole plate is perfectly in contact with the said card and the said sole plate, and provides excellent thermal transfer between the two.
The presence of the bearing surfaces prevents the material being crushed upon fixing and makes it possible to prevent any electrical contact between the card and the sole plate, while preserving the thermally conducting and electrically insulating properties for the intermediate material.
Advantageously, the printed circuit card features at least one thermal via in which the thermally conducting and electrically insulating material is accommodated, on which the printed circuit card and the sole plate exert a compression stress.
The presence of one or more thermal vias into which the intermediate material flows contributes to further enhancing the thermal exchanges.
The assembly according to the invention is, moreover, advantageously supplemented by the various following characteristics taken alone or according to all their technically possible combinations:
the fixing means which a bearing surface features comprise at least one crimping spike which interacts with a complementary orifice of the printed circuit card;
a crimping hole of the printed circuit card features metallisation in contact with the crimping spike; this metallisation provides for the earth to be taken up between the sole plate and the printed circuit card; it moreover provides stiffening for the printed circuit card in the crimping area;
the sole plate includes at least one counter-shape for accommodating at least one part of an element which extends in projection from the printed circuit card towards the sole plate;
the sole plate, in line with a bearing surface, carries cooling fins which extend in projection with respect to that face of the said sole plate which is opposite the printed circuit card;
the assembly includes a screening cap affixed to the sole plate in order to cover over the printed circuit card and the intermediate layer;
it includes a metal separation partition, and the printed circuit card carries, on one side of this metal partition, control electronics which particularly comprise a microprocessor and, on the other side of this partition, power electronics;
the metal partition is extended through the printed circuit card as far as the metal sole plate so as to define with it and the screening cap two chambers which are isolated from one another especially from electromagnetic disturbances.
According to another aspect of the invention there is provided a control module for a motor-vehicle headlight discharge lamp, and comprising an assembly of the first aspect of the invention.